Styrene and styrenic olefins are important materials used for a variety of applications, from organic synthesis of medicines, natural products, etc. to preparation of polystyrenic resins used in daily lives and industries. Especially, preparation of polystyrenic resins using styrenic olefins is industrially very important and is being actively investigated.
To take typical examples, there are homopolymers such as amorphous polystyrene (PS) resin, crystalline syndiotactic polystyrene (SPS), etc. and copolymers such as acrylonitrile-butadiene-styrene (ABS) resin, styrene-butadiene-styrene (SBS) resin, acrylonitrile-styrene-acrylate (ASA) resin, styrene-butadiene latex (SB latex), etc.
Researches on preparation of a variety of polystyrenic resins and researches on styrene and preparation of new styrenic olefins related with physical properties of polystyrenic resins are being performed and reported continuously.
Generally, styrene is prepared from dehydrogenation of ethylbenzene. In another method, 1-phenyl-ethanol is dehydrated to styrene using a dehydrating catalyst. So, most techniques are focusing on obtaining styrene from dehydration of 1-phenyl-ethanol.
The dehydration technique of 1-phenyl-ethanol known thus far can be performed both in gaseous and liquid phases. Non-homogeneous dehydrating catalysts comprising acidic materials can be used in both environments.
The most typical non-homogeneous dehydrating catalyst is a modified alumina It is the most frequently used in dehydration of 1-phenyl-ethanol. The dehydration condition for a liquid phase is usually 100-300° C. The usual gas phase dehydration condition is 210-330° C. and 0.1-10 atm.
WO 99/58,480 discloses dehydration under above conditions using catalysts with different particle sizes. U.S. Pat. No. 3,526,674 discloses dehydration in the presence of alumina catalysts and a variety of acidic catalysts. However, the reaction was successful only at an elevated temperature (200° C. or higher). Especially, preparation of styrenic olefins having substituents at a phenyl ring other than the styrene ring has never been reported.
Homogeneous catalysts are applicable only to the liquid phase. Of the homogeneous catalysts, p-toluenesulfonic acid is the most widely used. Cases of dehydrating 1-phenyl-ethanol to styrene under a mild liquid-phase condition using a catalyst obtained by adsorbing a metallic compound on silica gel were reported (J. Chem. Soc. Perkin Trans. I 1989, 707; Tetrahedron Letters, 1987, 28, 4565). But, when dehydration of alcohol was performed according to the methods presented in these papers, the reaction yield was not satisfactory (50% or less for most cases) and a lot of byproducts were generated.
Also, when the methods were applied to preparation of new styrenic olefins having substituents, such byproducts as ether dimer, oligostyrene, etc. were produced excessively. Because separation of these byproducts from styrenic olefin, or the target compound, is difficult, it raises an economic problem.